Enhanced PHICH transmission for LTE-advanced

ABSTRACT

A method is provided for communication in a wireless telecommunication system. The method comprises generating a sequence of signals of an enhanced physical HARQ (hybrid automatic repeat request) indicator channel (E-PHICH). The method further comprises mapping the sequence of signals of the E-PHICH to a first set of resource elements, wherein the first set of resource elements is multiplexed with a second set of resource elements over a set of virtual resource blocks, and wherein the second set of resource elements carries at least one of an enhanced physical downlink control channel (E-PDCCH) and a physical downlink shared channel (PDSCH).

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/545,525 filed on Jul. 10, 2012 entitled, “Enhanced PHICH Transmissionfor LTE-Advanced”, which claims priority to U.S. Provisional ApplicationNo. 61/607,436 filed Mar. 6, 2012 entitled, “Enhanced PHICH Transmissionfor LTE-Advanced”, which are incorporated by reference herein as ifreproduced in their entirety.

FIELD OF THE DISCLOSURE

The present disclosure relates to control channels in wirelesstelecommunications systems.

BACKGROUND

As used herein, the term “user equipment” (alternatively “UE”) might insome cases refer to mobile devices such as mobile telephones, personaldigital assistants, handheld or laptop computers, and similar devicesthat have telecommunications capabilities. Such a UE might include adevice and its associated removable memory module, such as but notlimited to a Universal Integrated Circuit Card (UICC) that includes aSubscriber Identity Module (SIM) application, a Universal SubscriberIdentity Module (USIM) application, or a Removable User Identity Module(R-UIM) application. Alternatively, such a UE might include the deviceitself without such a module. In other cases, the term “UE” might referto devices that have similar capabilities but that are nottransportable, such as desktop computers, set-top boxes, or networkappliances. The term “UE” can also refer to any hardware or softwarecomponent that can terminate a communication session for a user. Also,the terms “user equipment,” “UE,” “user agent,” “UA,” “user device,” and“mobile device” might be used synonymously herein.

As telecommunications technology has evolved, more advanced networkaccess equipment has been introduced that can provide services that werenot possible previously. This network access equipment might includesystems and devices that are improvements of the equivalent equipment ina traditional wireless telecommunications system. Such advanced or nextgeneration equipment may be included in evolving wireless communicationsstandards, such as long-term evolution (LTE). For example, an LTE systemmight include an Evolved Universal Terrestrial Radio Access Network(E-UTRAN) node B (eNB), a wireless access point, or a similar componentrather than a traditional base station. Any such component will bereferred to herein as an eNB, but it should be understood that such acomponent is not necessarily an eNB. Such a component may also bereferred to herein as an access node.

LTE may be said to correspond to Third Generation Partnership Project(3GPP) Release 8 (Rel-8 or R8) and Release 9 (Rel-9 or R9), and possiblyalso to releases beyond Release 9, while LTE Advanced (LTE-A) may besaid to correspond to Release 10 (Rel-10 or R10) and possibly also toRelease 11 (Rel-11 or R11) and other releases beyond Release 10. As usedherein, the terms “legacy”, “legacy UE”, and the like might refer tosignals, UEs, and/or other entities that comply with LTE Release 10and/or earlier releases but do not fully comply with releases later thanRelease 10. The terms “advanced”, “advanced UE”, and the like mightrefer to signals, UEs, and/or other entities that comply with LTERelease 11 and/or later releases. While the discussion herein deals withLTE systems, the concepts are equally applicable to other wirelesssystems as well.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of this disclosure, reference is nowmade to the following brief description, taken in connection with theaccompanying drawings and detailed description, wherein like referencenumerals represent like parts.

FIG. 1 is a diagram of a downlink LTE subframe, according to the priorart.

FIG. 2 is a diagram of an LTE downlink resource grid in the case of anormal cyclic prefix, according to the prior art.

FIG. 3 is a diagram of a mapping of a cell-specific reference signal ina resource block in the case of two antenna ports at an eNB, accordingto the prior art.

FIG. 4 is a diagram of a resource element group allocation in a resourceblock in the first slot when two antenna ports are configured at an eNB,according to the prior art.

FIG. 5 is a diagram of E-PDCCH regions, according to an embodiment ofthe disclosure.

FIG. 6 is a diagram of multiplexing an E-PHICH and an E-PDCCH withlocalized transmission, according to an embodiment of the disclosure.

FIG. 7 is a diagram of multiplexing an E-PHICH and an E-PDCCH withdistributed transmission, according to an embodiment of the disclosure.

FIG. 8 is a diagram of transmitting an E-PHICH in a common search space,according to an embodiment of the disclosure.

FIG. 9 is a diagram of multiplexing an E-PHICH and a PDSCH, according toan embodiment of the disclosure.

FIG. 10 is a diagram of allocating three virtual resource block pairsfor an E-PHICH, according to an embodiment of the disclosure.

FIG. 11 is a diagram of allocating one virtual resource block pair foran E-PHICH, according to an embodiment of the disclosure.

FIG. 12 is a diagram of an E-PHICH interleaving process, according to anembodiment of the disclosure.

FIG. 13 is a diagram of E-PHICH resource mapping, according to anembodiment of the disclosure.

FIG. 14 is another diagram of E-PHICH resource mapping, according to anembodiment of the disclosure.

FIG. 15 contains tables related to embodiments of the disclosure.

FIG. 16 is a simplified block diagram of an exemplary network elementaccording to one embodiment.

FIG. 17 is a block diagram with an example user equipment capable ofbeing used with the systems and methods in the embodiments describedherein.

FIG. 18 illustrates a processor and related components suitable forimplementing the several embodiments of the present disclosure.

DETAILED DESCRIPTION

It should be understood at the outset that although illustrativeimplementations of one or more embodiments of the present disclosure areprovided below, the disclosed systems and/or methods may be implementedusing any number of techniques, whether currently known or in existence.The disclosure should in no way be limited to the illustrativeimplementations, drawings, and techniques illustrated below, includingthe exemplary designs and implementations illustrated and describedherein, but may be modified within the scope of the appended claimsalong with their full scope of equivalents. Embodiments are describedherein in the context of an LTE wireless network or system, but can beadapted for other wireless networks or systems.

In an LTE system, physical downlink control channels (PDCCHs) are usedto carry downlink (DL) or uplink (UL) data scheduling information, orgrants, from an eNB to one or more UEs. The scheduling information mayinclude a resource allocation, a modulation and coding rate (ortransport block size), the identity of the intended UE or UEs, and otherinformation. A PDCCH could be intended for a single UE, multiple UEs orall UEs in a cell, depending on the nature and content of the scheduleddata. A broadcast PDCCH is used to carry scheduling information for aphysical downlink shared channel (PDSCH) that is intended to be receivedby all UEs in a cell, such as a PDSCH carrying system information aboutthe eNB. A multicast PDCCH is intended to be received by a group of UEsin a cell. A unicast PDCCH is used to carry scheduling information for aPDSCH that is intended to be received by only a single UE.

FIG. 1 illustrates a typical DL LTE subframe 110. Control informationsuch as the PHICH (physical HARQ (hybrid automatic repeat request)indicator channel), PCFICH (physical control format indicator channel),and PDCCH are transmitted in a control channel region 120. The PHICH isused to transmit HARQ acknowledgements and negative acknowledgements(ACK/NACK), which may indicate whether the eNB has correctly receiveduplink scheduled data on the physical uplink shared channel (PUSCH).

The control channel region 120 includes the first few OFDM (orthogonalfrequency division multiplexing) symbols in the subframe 110. The exactnumber of OFDM symbols for the control channel region 120 may bedynamically indicated by a control format indicator (CFI) in the PCFICH,which is transmitted in the first symbol. Alternatively, the number ofOFDM symbols may be semi-statically configured when cross carrierscheduling is configured in the case of carrier aggregation in LTERel-10.

The PDSCH, PBCH (physical broadcast channel), PSC/SSC (primarysynchronization channel/secondary synchronization channel), and CSI-RS(channel state information reference signal) are transmitted in a PDSCHregion 130. DL user data is carried by the PDSCH channels scheduled inthe PDSCH region 130. Cell-specific reference signals are transmittedover both the control channel region 120 and the PDSCH region 130, asdescribed in more detail below.

Each subframe 110 can include a number of OFDM symbols in the timedomain and a number of subcarriers in the frequency domain. An OFDMsymbol in time and a subcarrier in frequency together define a resourceelement (RE). A physical resource block (physical RB or PRB) can bedefined as, for example, 12 consecutive subcarriers in the frequencydomain and all the OFDM symbols in a slot in the time domain. An RB orPRB pair with the same RB index in slot 0 (140 a) and slot 1 (140 b) ina subframe can be allocated together.

FIG. 2 shows an LTE DL resource grid 210 within each slot 140 in thecase of a normal cyclic prefix (CP) configuration. The resource grid 210is defined for each antenna port, i.e., each antenna port has its ownseparate resource grid 210. Each element in the resource grid 210 for anantenna port is an RE 220, which is uniquely identified by an index pairof a subcarrier and an OFDM symbol in a slot 140. An RB 230 includes anumber of consecutive subcarriers in the frequency domain and a numberof consecutive OFDM symbols in the time domain, as shown in the figure.An RB 230 is the minimum unit used for the mapping of certain physicalchannels to REs 220.

For DL channel estimation and demodulation purposes, cell-specificreference signals (CRSs) can be transmitted over each antenna port oncertain pre-defined time and frequency REs in every subframe. CRSs areused by Rel-8 to Rel-10 legacy UEs to demodulate the control channels.FIG. 3 shows an example of CRS locations in a subframe for two antennaports 310 a and 310 b, where the RE locations marked with “R0” and “R1”are used for CRS port 0 and CRS port 1 transmission, respectively. REsmarked with “X” indicate that nothing should be transmitted on thoseREs, as CRSs will be transmitted on the other antenna.

Resource element groups (REGs) are used in LTE for defining the mappingof control channels such as the PDCCH to REs. A REG includes either fouror six consecutive REs in an OFDM symbol, depending on whether the CRSsare included. For example, for the two-antenna port CRSs shown in FIG.3, the REG allocation in each RB is shown in FIG. 4, where the controlregion 410 includes two OFDM symbols and different REGs are indicatedwith different types of shading. REs marked with “R0” or “X” in FIG. 4aor with “R1” or “X” in FIG. 4b are reserved for CRSs for antenna port 0and antenna port 1, and therefore only four REs in each REG areavailable for carrying control channel data.

A PDCCH can be transmitted on an aggregation of one or more consecutivecontrol channel elements (CCEs), where one CCE consists of, for example,nine REGs. The CCEs available for a UE's PDCCH transmission are numberedfrom 0 to n_(CCE)−1. In LTE, multiple formats are supported for thePDCCH as shown in Table 1 in FIG. 15.

The number of CCEs available in a subframe depends on the systembandwidth and the number of OFDM symbols configured for the controlregion. For example, in a 10 MHz system with three OFDM symbolsconfigured for the control region and six groups configured for thePHICH, 42 CCEs are available for the PDCCH.

Multiple PDCCHs may be multiplexed in the control region in a subframeto support UL and DL data scheduling for one UE and to support DL and ULscheduling for more than one UE. For a given system bandwidth, thenumber of PDCCHs that can be supported in the control region alsodepends on the aggregation level used for each PDCCH. The aggregationlevel indicates how many CCEs are aggregated to carry a PDCCH. Theaggregation level for a given target packet error rate is determined bythe downlink received signal quality at a UE and the size of thedownlink control information (DCI) to be carried by a PDCCH. In general,a high aggregation level is needed for a PDCCH intended for a UE that isat the cell edge and is far away from the serving eNB, or when a DCIwith a large payload size is used.

The legacy PDCCH region in LTE may have capacity issues for some newapplications or deployment scenarios where the number of scheduled UEsin a subframe could be large. Some examples include multiple usermultiple input multiple output (MU-MIMO) transmission, coordinatedmulti-point (CoMP) transmission, heterogeneous network (hetnet)deployment with remote radio heads (RRHs) in a cell sharing the samecell ID, and carrier aggregation (CA). With these deployment scenarios,there may be a need to enhance the capacity of the PDCCH and at the sametime to limit the number of blind decodes required by an advanced UE.

One approach for PDCCH capacity enhancement is to transmit DCI in thelegacy PDSCH region. That is, some RBs or PRB pairs in the traditionalPDSCH region can be reserved for DCI transmission to UEs. Hereinafter, aphysical downlink control channel transmitted in the legacy PDSCH regionwill be referred to as an extended or enhanced PDCCH (E-PDCCH). A set ofRBs and OFDM symbols or PRB pairs reserved for this purpose can bereferred to as an E-PDCCH region. The E-PDCCH region in a subframe isnot necessarily completely filled with E-PDCCHs in that some resourcesin the E-PDCCH region not used for E-PDCCH transmission can be assignedfor PDSCH transmission. In addition, for some scenarios, the legacyPDCCH region may or may not be present in a subframe containing anE-PDCCH region. The time and frequency resources of an E-PDCCH regionmay be configurable. Examples of E-PDCCH regions are shown in FIG. 5.

Multiple PHICHs may be transmitted in the same set of resource elementsand may be defined as a PHICH group. In the same PHICH group, multiplePHICHs may be multiplexed with different complex orthogonal Walshsequences. In the case of a normal cyclic prefix, eight PHICHs can bemultiplexed within a PHICH group, as the length of the orthogonalsequence is four and the PHICHs are also multiplexed over the I and Qbranches. Meanwhile, four PHICHs can be multiplexed within a PHICH groupwith length-2 Walsh sequences.

For PHICH resource configuration, two parameters are signaled in themaster information block (MIB): the PHICH duration and the number ofPHICH groups. The duration of the PHICH specifies the number of OFDMsymbols that the PHICH is distributed over. To avoid dependency with thePCFICH, the duration is independently signaled and can be different fromthe control region for the PDCCH. The second parameter is used to definethe amount of PHICH resources, i.e., the number of PHICH groups. Themapping between PHICH resources and the corresponding uplink scheduledtransmission is implicit. That is, there is a predefined mapping rulebetween the PHICH resource index and the PUSCH PRB index transmittingthe uplink shared channel. Because there can be a PUSCH transmissionwithout a PDCCH, e.g., in the case of resource non-adaptiveretransmission, the PHICH resource is mapped to the actual PUSCH PRBindex instead of the PDCCH CCE index.

A PHICH resource is identified by the index pair (n_(PHICH) ^(group),n_(PHICH) ^(seq)) where n_(PHICH) ^(group) is the PHICH group number andn_(PHICH) ^(seq) is the orthogonal sequence index within the group. As aPHICH resource is implicitly defined by the lowest PRB index in thefirst slot of the corresponding PUSCH transmission, the UE derives theassigned index pair with the scheduled PUSCH PRB index. If the PHICHresource is smaller than the number of PUSCH PRBs or if multiple usersare scheduled in the same PUSCH PRBs, a collision can happen. That is,the same PHICH resource may be assigned to multiple UEs. To avoid acollision, a different cyclic shift value, which is indicated in theuplink DCI format, may be used to derive the assigned PHICH resource.More specifically, the following equation may be used to determine theindex pair.n _(PHICH) ^(group)=(I _(PRB) _(_) _(RA) ^(lowest) ^(_) ^(index) +n_(DMRS))modN _(PHICH) ^(group) +I _(PHICH) N _(PHICH) ^(group)  (1)n _(PHICH) ^(seq)=(└I _(PRB) _(_) _(RA) ^(lowest) ^(_) ^(index) /N_(PHICH) ^(group) ┘+n _(DMRS))mod2N _(SF) ^(PHICH)  (2)

In the above equation, n_(DMRS) is mapped from the cyclic shift for thedemodulation reference signal (DMRS) field in the most recent DCI format0 or 4 for the transport block associated with the corresponding PUSCHtransmission. n_(DMRS) is set to zero if there is no PDCCH with DCIformat 0 or 4 for the same transport block and if the initial PUSCH forthe same transport block is semi-persistently scheduled or the initialPUSCH for the same transport block is scheduled by the random accessresponse grant. N_(SF) ^(PHICH) is the spreading factor size used forPHICH modulation as described in section 6.9.1 of 3GPP TechnicalSpecification (TS) 36.213. I_(PRB) _(_) _(RA) ^(lowest) ^(_) ^(index) isthe lowest PRB index in the first slot of the corresponding PUSCHtransmission. N_(PHICH) ^(group) is the number of PHICH groupsconfigured by higher layers as described in section 6.9 of 3GPP TS36.213.

$I_{PHICH} = \left\{ \begin{matrix}1 & {\mspace{11mu}\begin{matrix}{{for}\mspace{14mu}{TDD}\mspace{14mu}{{UL}/{DL}}\mspace{14mu}{configuration}\mspace{14mu} 0\mspace{14mu}{with}} \\{{{PUSCH}\mspace{14mu}{transmission}\mspace{14mu}{in}\mspace{14mu}{subframe}\mspace{20mu} n} = {4\mspace{14mu}{or}\mspace{14mu} 9}}\end{matrix}\;} \\0 & {otherwise}\end{matrix} \right.$

The E-PDCCH specified in LTE Rel-11 systems may support increasedcontrol channel capacity, may support frequency domain inter-cellinterference coordination (ICIC), may achieve improved spatial reuse ofcontrol channel resources, may support beamforming and/or diversity, mayoperate on advanced carrier types and in MBSFN subframes, and maycoexist on the same carrier with legacy UEs. In some cases, the E-PDCCHmay be transmitted by using PDSCH resources, so the introduction of theE-PDCCH may have no impact on legacy PDCCH transmissions. Further, theE-PDCCH may increase control channel capacity by borrowing PDSCHresources.

To support frequency domain ICIC and to multiplex with the PDSCH, theE-PDCCH may be transmitted within downlink PRBs or PRB pairs instead ofbeing spread over the entire system bandwidth. In the time domain, ifthe E-PDCCH is distributed over the subframe in the PDSCH region,additional signaling may not be necessary. Otherwise, the number of OFDMsymbols may need to be signaled. The E-PDCCH region in the frequencydomain and time domain may be signaled with radio resource control (RRC)signaling or dynamic signaling.

The E-PDCCH region may be multiplexed with the PDSCH only in thefrequency domain. Therefore, E-PDCCHs may be transmitted in differentPRBs or PRB pairs from the PRB pairs on which PDSCHs are transmitted.Alternatively, the E-PDCCH and the PDSCH may be transmitted in the samePRB or PRB pair by dividing the number of OFDM symbols in the timedomain.

Both localized and distributed transmission may be supported for theE-PDCCH. At least for localized transmission, and for distributedtransmission where the CRS is not used for demodulation of the enhancedcontrol channel, the demodulation of the enhanced control channel may bebased on the DMRS transmitted in the PRBs or PRB pairs used fortransmission of the E-PDCCH.

Given that the E-PDCCH has been introduced because the capacity of thePDCCH may be insufficient, an issue that may arise is whether thecapacity of the legacy PHICH is sufficient. In a Rel-8 LTE system, thenumber of PHICHs is dependent on the number of PRBs, the number oforthogonal sequences, and the parameter N_(g) where N_(g) ϵ{⅙, ½, 1, 2}is provided by higher layers. For example, in case of 20 MHz and thenormal cyclic shift, the maximum number of PHICHs is 200 if N_(g) isconfigured as 2. Meanwhile, in the case of the PDCCH, the maximum numberof PDCCHs is 88, assuming that the PDCCH aggregation level is 1 and thatthree OFDM symbol are used for the control region. According to thisbrief calculation, it can be seen that the maximum number of PHICHresources is approximately double of the number of PRBs in the samesystem bandwidth. However, although the number of PHICH resources islarger than the PDCCH resource capacity, increasing the PHICH capacitymay be important in some scenarios. For example, when an additionalcarrier without a control region is supported or when a control channelexperiences strong interference, the PHICH for the additional carriermay need to be transmitted on the primary carrier. Another example isthe scenario where remote radio heads (RRHs) with the same cell ID asthe macro eNB are supported. In this case, the number of UEs scheduledto transmit the PUSCH may be dramatically increased. Furthermore, thecurrent PHICH structure may not be efficient for frequency domain ICICbecause the PHICH is distributed over the entire system bandwidth.

Embodiments of the present disclosure provide a detailed design for anextended or enhanced PHICH (E-PHICH) structure, including resourceallocation and multiplexing between the E-PHICH and the E-PDCCH. Morespecifically, at least four issues related to the E-PHICH areidentified, and at least one set of embodiments is disclosed for each ofthe issues. The embodiments will be briefly summarized, and then detailswill be provided for each set of embodiments.

The first set of embodiments deals with multiplexing of the E-PHICH withthe E-PDCCH or the PDSCH. Five different approaches are provided in thisfirst set of embodiments. In a first approach, E-PHICHs may betransmitted with localized E-PDCCH transmission in the same PRBs or PRBpairs as the PRBs used for the E-PDCCHs. In a second approach, E-PHICHsmay be transmitted in PRBs or PRB pairs for E-PDCCHs configured withdistributed transmission. In a third approach, E-PHICHs may betransmitted in PRBs or PRB pairs where commonly monitored E-PDCCHs aretransmitted. A common search space may be defined for E-PDCCHs totransmit DCI formats aimed to all UEs or group of UEs. E-PHICHs may bemultiplexed with E-PDCCHs in the PRBs or PRB pairs reserved for thecommon search space. In a fourth approach, E-PHICHs may be transmittedin PRBs or PRB pairs for PDSCH transmission. An E-PHICH may betransmitted in a different PRB or PRB pair from an E-PDCCH. In order toavoid wasting resources when all REs are not used for PHICH resources,the E-PHICH may be multiplexed with the PDSCH in the same PRBs or PRBpairs. In a fifth approach, an E-PHICH may be transmitted alone inseparate virtual resource blocks (VRBs). Different E-PHICH groups may bemultiplexed and interleaved before mapping across VRBs. The VRBs maythen be mapped to PRBs in a distributed manner. Frequency hopping may beapplied to the second slot of the VRBs.

The second set of embodiments deals with resource allocation for theE-PHICH. Multiple PHICH resource sets may be defined to efficientlyutilize E-PHICH resources. Each PHICH resource set can be mapped to aPUSCH PRB index. The actually used E-PHICH resource set may beexplicitly indicated with semi-static signaling or dynamic signaling.Alternatively, the actually used E-PHICH resource may be implicitlyindicated with a CCE index of the E-PDCCH or PDCCH transmitting theuplink grant.

The third set of embodiments deals with monitoring and receiving thePHICH and the E-PHICH. When both the PHICH in the legacy control regionand the E-PHICH are supported and configured, the UE may monitor andreceive both the PHICH and the E-PHICH. In this case, the actual PHICHor E-PHICH resource may be determined depending on the PUSCH PRB indexand the DMRS cyclic shift, where the number of E-PHICHs that aresupported could be signaled or re-interpreted from the PBCH or signaledthrough higher layer signaling. Alternatively, the UE may receive theE-PHICH only if the UE is configured to monitor the E-PDCCH region or ifthe eNB configures the UE to receive the E-PHICH only.

The fourth set of embodiments deals with inter-cell interferencemanagement for the E-PHICH. To avoid interference in E-PHICHtransmissions between neighbor cells, inter-cell interferencecoordination may be supported for E-PHICH transmissions. In oneembodiment, a signal related to a PHICH resource may be exchangedbetween cells, and the E-PHICH resource parameter may be signaled to theconnected UEs. The detailed E-PHICH procedure may depend on whether thelegacy control region is supported or not.

Details about each of these four sets of embodiments will now beprovided.

In the first approach under the first set of embodiments dealing withmultiplexing of the E-PHICH and the E-PDCCH or the PDSCH, E-PHICHs aretransmitted in VRBs for E-PDCCHs configured with localized transmission.In localized E-PDCCH transmission, an E-PDCCH is transmitted in eitherone or multiple consecutive VRBs that are not used for transmission ofother E-PDCCHs. Since one E-PDCCH is transmitted within one or multiplePRBs (or PRB pairs) and precoded DMRS is used, interleaving betweenmultiple E-PDCCHs as used in the legacy PDCCH may not be supported inlocalized E-PDCCH transmissions. The VRBs may be mapped to PRBs, whichmay be either consecutive or non-consecutive in frequency.

FIG. 6 shows one example of multiplexing the E-PHICH and the E-PDCCHwith localized transmission. Two E-PDCCHs 610 and 620 that aretransmitted in separate PRB pairs are illustrated. Two E-PHICH groups630 and 640 are shown, each of which contains multiple units (as thePHICH is repeated three times as defined in Rel-8), and these units arespread across the whole E-PDCCH region. For localized E-PDCCHtransmission, as precoding could be applied to both the E-PDCCH and thecorresponding DMRS, the precoded DMRS may not be suitable for decodingthe E-PHICH because the E-PHICH may contain ACK/NACKs for multiple UEs.In this case, a common reference signal, such as the CRS or atransmission point (TP)-specific reference signal that is not precoded,may be used for E-PHICH decoding. However, if three repetitions of anE-PHICH group are transmitted in separate PRB pairs, a precoded DMRS maystill be used to decode the E-PHICH because the precoding vectors usedin each PRB pair may not be the same, thus creating some spatialdiversity in addition to frequency/time diversity.

While a region may be semi-statically defined for localized E-PDCCHtransmission, not all the PRB pairs may carry the E-PDCCH at all times.Thus, it is possible that some of the PRB pairs defined in a region forlocalized E-PDCCH may be used to carry the PDSCH in some subframes. Insuch a situation, the E-PHICH could still be transmitted in these PRBpairs. If the PDSCHs transmitted in such PRB pairs are for legacy UEs,the UEs may not be aware of the E-PHICH, and data may be punctured,which could degrade the PDSCH performance. If the PDSCHs transmitted insuch PRB pairs are for Rel-11 or beyond UEs, rate matching may beapplied to those REs reserved for the E-PHICH. In either case, Rel-11 orbeyond UEs may still expect to receive the E-PHICH in these PRB pairs.

If a distributed E-PDCCH transmission is defined as to transmit anE-PDCCH on PRBs or maybe even smaller units, and such PRBs or units fortransmitting the same E-PDCCH are distributed across a wide frequencybandwidth, the E-PHICH transmission may be multiplexed in a similar wayas it is multiplexed with an E-PDCCH with a localized E-PDCCHtransmission.

In the second approach under the first set of embodiments dealing withmultiplexing of the E-PHICH and the E-PDCCH or the PDSCH, E-PHICHs aretransmitted in VRBs for E-PDCCHs configured with distributedtransmission. For an E-PDCCH with distributed transmission, multipleE-PDCCHs may be multiplexed and interleaved together and transmitted onthe same VRBs. Given that a higher reliability is generally needed forHARQ-ACK transmissions than for scheduling grants and that the sameE-PHICH time/frequency resource may be shared by multiple UEs with anorthogonal Walsh sequence, a distributed transmission may be moresuitable than a localized transmission for the E-PHICH to achieve morefrequency diversity instead of frequency selectivity. Therefore, insteadof transmitting the E-PHICH in all distributed and localized E-PDCCHresource regions, the E-PHICH may be multiplexed with the E-PDCCH andmay be configured only with distributed transmission and use anon-precoded DMRS for decoding. As shown in FIG. 7, two E-PDCCHs 710 and720 are multiplexed and transmitted on the same PRB pairs, and twoE-PHICH groups 730 and 740 are transmitted from the same PRB pairs asthe E-PDCCH.

If E-PDCCH resources are RRC configured, then the E-PHICH may bemultiplexed together with the distributed E-PDCCH (cross-interleaved).Two regions may be configured for the E-PDCCH, one distributed and theother localized. Although two regions may be configured, it is possiblethat only the distributed E-PDCCH region contains E-PHICH resources. AUE may be configured to do E-PDCCH blind decoding in one or both regions(i.e., distributed only, localized only, or both). However, all UEs mayneed to decode the E-PHICH in a distributed E-PDCCH region if a HARQ-ACKis expected, because the E-PHICH may be transmitted only in thedistributed E-PDCCH region in this case.

In the distributed E-PDCCH region, some resources may be configured forthe E-PHICH. REGs could be defined over the VRBs, and some REGs may befor the E-PHICH only. E-PHICH groups may be similarly defined as in thelegacy PHICH. The rest of the REGs may then be grouped into CCEs andused for the E-PDCCH.

A reference signal for demodulation may be shared in the region. Eithera CRS or a non-precoded DMRS may be used. In the case of a DMRS, thenumber of DMRS ports may be the same as the number of CRS ports asindicated by decoding the PBCH. Alternatively, the number of DMRS portsmay be different from the number of CRS ports and may be configured byRRC signaling. Different DMRS ports or sequence may be configured andused in different cells.

The REG definition in OFDM symbols with a DMRS and/or a CSI-RS may needto be modified, as the REs in an OFDM symbol may not be an even numberor multiples of four REs. One alternative for REG definition in thoseOFDM symbols may be to define a REG as a 2RE×2RE square unit thatoccupies two consecutive REs in the frequency domain and two consecutiveREs in the time domain. In another alternative, a REG could be dividedinto two pairs of REs, each consisting of two consecutive REs in thefrequency domain. These two pairs of REs could be consecutivelyallocated along frequency, but in the case where there are not enoughREs left in an OFDM symbol, the second pair could start from the nextOFDM symbol. The allocation of REs for an E-PHICH REG may skip those REsreserved for DMRS or CSI-RS transmission. If there is only one orphan REleft in an OFDM symbol, the RE may be skipped.

Transmit diversity may be used, and random beamforming may also bepossible, either on a per-RB or a per-REG basis, but precoding vectorsmay need to be predefined in case of per-REG beamforming.

In the third approach under the first set of embodiments dealing withmultiplexing of the E-PHICH and the E-PDCCH or the PDSCH, E-PHICHs aretransmitted in VRBs for E-PDCCHs that are commonly monitored. That is,it may be possible to multiplex an E-PHICH with an E-PDCCH monitored byall UEs or group of UEs, for instance in a common search space. Forexample, the E-PHICH may be transmitted in the same VRBs configured asthe common search space for the E-PDCCH as shown in FIG. 8. Theresources used to transmit the E-PHICH may be pre-defined and known tothe UE. The resources may be interleaved with the E-PDCCHs that carrythe common message. The UE may only need to decode the E-PHICH when theUE expects ACK/NACK signals. For the E-PHICH, transmit diversity may beused and/or a non-precoded DMRS may be used as a reference signal.

In the fourth approach under the first set of embodiments dealing withmultiplexing of the E-PHICH and the E-PDCCH or the PDSCH, E-PHICHs aretransmitted in PRB pairs for PDSCH transmission. In this case, E-PHICHresources may be within the resources used for the PDSCH. That is, theE-PHICH may be multiplexed with the PDSCH in the same PRB pairs. ThePRBs used for the E-PHICH may be defined similarly to the way theE-PDCCH regions are defined. For example, the number and location ofE-PHICH RBs may be signaled to advanced UEs or may be predefined.

The maximum number of resource elements required for the legacy PHICH iscalculated in Table 2 in FIG. 15 with respect to the system bandwidth.Table 3 in FIG. 15 shows available resource elements in a PRB pair in asubframe for PDSCH data transmission for different control regionconfigurations and four CRS ports. Assuming the same or a similar amountof PHICH resources may need to be supported in the E-PHICH, then amaximum of three PRB pairs may be needed for 20 MHz, and less than onePRB pair may be needed for 5 MHz or less.

Given the number of REs in one PRB pair as shown in Table 3, thegranularity for E-PHICH resources may be coarse if only the E-PHICH istransmitted in a PRB pair. To avoid wasting resources while providingsufficient diversity in frequency and/or time, the E-PHICH may be mappedto REs that are otherwise used for PDSCH transmission, as illustrated inFIG. 9. The manner in which the E-PHICHs are mapped in the PDSCH may bepre-defined or configured through higher signaling. The E-PHICH may takeresources in units of REG in a similar way as the legacy PHICH does inthe PDCCH region. The unit REG may be composed of, e.g., four closelylocated REs. Since the E-PHICH may be spread out and may not be requiredto take as many REs within a PRB pair as possible, higher-orderdiversity may be achieved, which may lead to better performance of thePHICH.

There are at least two options for the PDSCH in terms of how to takeinto account the REs that are reserved for E-PHICHs. If the PDSCHs areused for legacy UEs, puncturing of the PDSCHs at the RE locationsconfigured for E-PHICHs may be used to ensure that legacy UEs can stillreceive the PDSCH. If the PDSCHs are used for advanced UEs only, thenrate matching may be applied to take into account the REs reserved forE-PHICHs.

As an E-PHICH group may contain PHICHs for multiple UEs, the referencesignal used for decoding may need to be a common reference signal, suchas a cell-specific reference signal or a TP-specific reference signal.Such a reference signal may be different from the reference signal forPDSCH decoding, which could be precoded.

In the fifth approach under the first set of embodiments dealing withmultiplexing of the E-PHICH and the E-PDCCH or the PDSCH, E-PHICHs aretransmitted in their own VRBs. That is, an E-PHICH may be transmitted ina VRB that is used only to carry HARQ ACK/NACK signals. As seen fromTable 2 and Table 3 in FIG. 15, for a system bandwidth of 5 MHz to 20MHz, the required number of REs for the E-PHICH is in the range of REsthat can be carried by one to three PRB or VRB pairs. So one to threePRBs in both slots could be assigned to transmit the E-PHICH only in thelegacy PDSCH region. Table 4 in FIG. 15 shows the possible number of VRBpairs that may be used to carry an E-PHICH-only transmission fordifferent system bandwidths.

Similar to the PHICH, each E-PHICH may consist of three REGs, whichrepresent its three repetitions. As shown in FIG. 10, REGs carrying oneE-PHICH group may be multiplexed and interleaved with REGs of otherE-PHICH groups and mapped across assigned VRBs in both slots that onlycarry an E-PHICH. These VRBs in both slots may then be mapped to PRBs indistributed manners across the whole system bandwidth, thus creatingmore frequency diversity gain. If there is only one pair of VRBs in bothslots of a subframe configured, as shown in FIG. 11, in order to stillmaintain necessary frequency diversity, hopping operation may be appliedto the VRB in the second slot (i.e., a VRB of the distributed type), sothat the VRBs are transmitted at different frequencies in the first andsecond slots. As the VRB configuration parameters (e.g., distributed vslocalized, gap 1 vs gap 2) can be shared between multiple commondownlink control channels, such as the E-PHICH and the common searchspace of the E-PDCCH, such parameters may be signaled once for allrelevant enhanced downlink control channels.

For the interleaving process, as shown in FIG. 12 as an example, REGs ofdifferent E-PHICH groups may be lined up according to their E-PHICHgroup number. A REG-based interleaver, such as a row-in/column-out blockinterleaver, may be applied, whose output is REGs from different E-PHICHgroups in mixed order.

In an embodiment, 2-tx and 4-tx transmit diversity (TxD) based onAlamouti coding may be applied to an E-PHICH transmission. Theconfiguration of antenna number for TxD may be signaled to the UE or maybe implied by another configuration, such as that for distributedE-PDCCH transmission. A CRS may be used for decoding the E-PHICH in sucha transmission. Alternatively, a DMRS without channel dependentprecoding may be used for this purpose. If hopping is applied to thesecond slot (i.e., DVRB), the DMRS may need to be re-designed to ensurethat the performance of the E-PHICH is maintained, especially in highmobility situations.

The location of such PRB pairs for E-PHICH-only transmission may varyfor different cells or TPs to avoid collisions of E-PHICHs fromdifferent cells and TPs. One way to implement this variance is to linkthe locations of PRB pairs for the E-PHICH to the cell ID or anadditional or alternative parameter distinct to each TP.

The configuration of an E-PHICH-only transmission may be semi-staticallysignaled to the UE through higher layer signaling, such as RRCsignaling. The configuration may include parameters such as the numberof VRB used, the VRB-to-PRB mapping, the location where the second slotis hopped to, the transmit mode (e.g., TxD), the number of transmitantennas, and the corresponding reference signal ports for decoding.

A benefit of configuring VRBs for E-PHICH-only transmission is thatE-PHICH transmission could be configured independently from that of theE-PDCCH, especially for the case where only a localized E-PDCCH regionis defined and a pre-coded DMRS is used for the E-PDCCH.

As mentioned previously, a second set of embodiments deals with resourceallocation for the E-PHICH. In existing LTE systems, one PHICH resourceset is defined in a cell, and a PHICH resource (i.e., an index pair of aPHICH group and orthogonal sequence index in the group) is implicitlymapped to the starting index of the PRBs of a scheduled PUSCH. In anembodiment, multiple PHICH/E-PHICH resource sets are provided toincrease PHICH capacity, while efficiently utilizing E-PHICH resources.An E-PHICH resource set is a collection of E-PHICH resources, where eachE-PHICH resource is capable of carrying one E-PHICH that corresponds toa previous PUSCH transmission. The individual resource in the resourceset is specified by a resource index. One example of a resource index isthe index pair (n_(PHICH) ^(group), n_(PHICH) ^(seq)) where n_(PHICH)^(group) is the PHICH group number and n_(PHICH) ^(seq) is theorthogonal sequence index within the group. E-PHICH resources within aset can be mapped to all PUSCH PRB indices. FIG. 13 shows E-PHICHresources mapping to PUSCH PRBs logically. In this figure, it is assumedthat the number of PHICHs in an E-PHICH resource set is equal to thenumber of PUSCH PRBs. If the number of PHICHs in an E-PHICH resource setis smaller than the number of PUSCH PRBs, different DMRS cyclic shiftsmay be signaled to different PUSCHs in order to avoid collisions in theactual PHICH transmissions. As shown in FIG. 13, for one PUSCH PRB, twoE-PHICHs can be mapped in E-PHICH resource set #1 and set #2.

Collisions between E-PHICH resources assigned to multiple UEs can happenwhen the number of E-PHICH resources is smaller than the number of PUSCHPRBs or when multiple UEs are allocated with the same PUSCH PRB, in thecase of multiple-user multiple input/multiple output (MU-MIMO) forexample. In such a case, different cyclic shifts may be signaled toavoid collision.

Multiple E-PHICH PRB resource sets may be useful in the scenario wheremultiple E-PHICHs are multiplexed with different types of E-PDCCHregions. For example, E-PHICH resource set 1 may be multiplexed with anE-PDCCH configured with localized transmission, while E-PHICH resourceset 2 may be multiplexed with an E-PDCCH configured with distributedtransmission. In this case, if a UE is configured to monitor thelocalized E-PDCCH region, the UE may need to monitor and receive theE-PHICH in E-PHICH resource set 1 only when a PUSCH PRB is scheduled byan E-PDCCH localized transmission. Otherwise, if a UE is configured tomonitor the distributed E-PDCCH region, the UE may need to monitor andreceive the E-PHICH in E-PHICH resource set 2 only when a PUSCH PRB isscheduled by an E-PDCCH distributed transmission. This may reduce UEcomplexity by not receiving the E-PHICH over all E-PHICH resources.

Multiple E-PHICH PRB resource sets may also be useful in the scenariowhere multiple reference signal structures or transmission schemes maybe required. For example, when multiple RRHs are configured with thesame cell ID and E-PHICHs are transmitted in different RRHs withdifferent reference signals, it may be desirable to receive the E-PHICHfrom an RRH suitable for the UE. In this case, a separate E-PHICHresource set may be configured for each RRH.

Multiple E-PHICH PRB resource sets may also be useful in the scenariowhere saving the resources reserved for the E-PHICH may be required.Although an E-PHICH resource may be mapped to a PUSCH PRB index, thesame amount of E-PHICH resources as the number of PUSCH PRBs may not berequired because multiple PRBs can be scheduled to one UE. In Rel-8, theamount of PHICH resources is configured with the PBCH, and hence may bedifficult to change, depending on the number of actually required PHICHresources. If the E-PHICH resource set is dynamically indicated in theuplink grant, it may be possible to reduce the resources reserved forthe E-PHICH by assigning the E-PHICH to a certain E-PHICH group only.Therefore, depending on the number of UEs scheduled for PUSCHtransmission, all E-PHICH transmissions may be limited to one E-PHICHresource set, and the remaining E-PHICH resource sets may be used forPDSCH transmissions.

Multiple E-PHICH resource sets may be assigned in different frequency,time or code sequence domains. In FIG. 13, two E-PHICH resource sets areconfigured, and the E-PHICH in each set is mapped to a PUSCH PRB.

It is not necessarily required to reserve twice the amount of theE-PHICH resources and map the resources to PUSCH PRBs in each E-PHICHresource set, because multiple PUSCH PRBs may be allocated to one UE andonly one or two PHICH resources may be required to transmit one or twoHARQ ACKs.

The actually used E-PHICH resource set may be either semi-staticallyconfigured or dynamically indicated by including E-PHICH resource setinformation explicitly in an uplink grant. For example, if the maximumfour E-PHICH resource sets are supported, two bits of information may beincluded to indicate which E-PHICH resource set is used. Alternatively,implicit indication is also possible, where the CCE or eCCE index of theE-PDCCH carrying the uplink grant may be used to derive the E-PHICHresource set. Let {S₀, S₁, . . . , S_(M-1)} be the M sets of E-PHICHresources and n be the lowest CCE or eCCE index of an E-PDCCH carryingan uplink grant for PUSCH transmission. Then, as an example, the E-PHICHresource set S_(k) for the corresponding E-PHICH can be implicitlyderived using the following equation (3).k=nmodM  (3)

Once the E-PHICH resource set is determined, the existing PHICH equationmay be reused to calculate the E-PHICH group and orthogonal sequenceindex pair within each E-PHICH resource set. In this case, N_(PHICH)^(group) may be the number of PHICH groups in the corresponding E-PHICHresource set.

As mentioned previously, a third set of embodiments deals withmonitoring and receiving the PHICH and the E-PHICH. If both legacycontrol regions and the E-PHICH are supported and configured, anadvanced UE may monitor and receive both the PHICH and the E-PHICH. Ifan advanced UE is configured to receive both the PDCCH and the E-PDCCH,the UE may also be able to receive both the PHICH and the E-PHICH. Inthis case, all PHICH and E-PHICH resources may be jointly mapped to aPUSCH PRB index. For a UE receiving both the PHICH and the E-PHICH, theequation for deriving a PHICH resource may need to be modified. Forexample, two parameters may be signaled for the PHICH group number ofgroups for the PHICH (N_(PHICH) ^(group)) and for the E-PHICH (N_(PHICH)^(group)), respectively. The PHICH group index may be calculated by:n _(PHICH) ^(group)=(I _(PRB) _(_) _(RA) ^(lowest) ^(_) ^(index) +n_(DMRS))mod(N _(PHICH) ^(group) +N _(E-PHICH) ^(group))+I _(PHICH)(N_(PHICH) ^(group) +N _(E-PHICH) ^(group))  (4)n _(PHICH) ^(seq)=(└I _(PRB) _(_) _(RA) ^(lowest) ^(_) ^(index)/(N_(PHICH) ^(group) N _(E-PHICH) ^(group))┘+n _(DMRS))mod2N _(SF)^(PHICH)  (5)

In order to know whether the PHICH or the E-PHICH is used, the UE maycompare the calculated n_(PHICH) ^(group) with N_(PHICH) ^(group).Specifically, the UE may know that the E-PHICH resource is used ifn_(PHICH) ^(group) is larger than or equal to N_(PHICH) ^(group). As thenumber of groups for the PHICH (N_(PHICH) ^(group)) is already indicatedin the PBCH, the number for an E-PHICH group (N_(E-PHICH) ^(group)) maybe signaled in the PBCH using unused bits. Alternatively, the number foran E-PHICH group may be signaled by higher layer signaling.

Alternatively, a PHICH or E-PHICH resource may be used depending on thePUSCH PRB index and whether a DMRS value meets certain criteria. Forexample,If |(I _(PRB) _(_) _(RA) ^(lowest) ^(_) ^(index) +n _(DMRS))/2N _(SF)^(PHICH) |>N _(PHICH) ^(group),n _(E-PHICH) ^(group)=(I _(PRB) _(_) _(RA) ^(lowest) ^(_) ^(index) +n_(DMRS))modN _(E-PHICH) ^(group) +I _(PHICH) N _(E-PHICH) ^(group)  (6)n _(E-PHICH) ^(seq)=(└I _(PRB) _(_) _(RA) ^(lowest) ^(_) ^(index) /N_(E-PHICH) ^(group) ┘+n _(DMRS))mod2N _(SF) ^(PHICH)  (7)else,n _(PHICH) ^(group)=(I _(PRB) _(_) _(RA) ^(lowest) ^(_) ^(index) +n_(DMRS))modN _(PHICH) ^(group) +I _(PHICH) N _(PHICH) ^(group)  (8)n _(PHICH) ^(seq)=(└I _(PRB) _(_) _(RA) ^(lowest) ^(_) ^(index) /N_(PHICH) ^(group) ┘+n _(DMRS))mod2N _(SF) ^(PHICH)  (9)

Instead of jointly mapping the PHICH and E-PHICH resources, it is alsopossible that the PHICH may be used when an uplink DCI grant istransmitted on the PDCCH and that the E-PHICH may be used when an uplinkDCI grant is transmitted on the E-PDCCH. In this case, the PHICH groupindex equation can be defined as follows.

If an uplink DCI grant is transmitted on a PDCCH,n _(PHICH) ^(group)=(I _(PRB) _(_) _(RA) ^(lowest) ^(_) ^(index) +n_(DMRS))modN _(PHICH) ^(group) +I _(PHICH) N _(PHICH) ^(group)  (10)n _(PHICH) ^(seq)=(└I _(PRB) _(_) _(RA) ^(lowest) ^(_) ^(index) /N_(PHICH) ^(group) ┘+n _(DMRS))mod2N _(SF) ^(PHICH)  (11)

else if an uplink DCI grant is transmitted on an E-PDCCH,n _(E-PHICH) ^(group)=(I _(PRB) _(_) _(RA) ^(lowest) ^(_) ^(index) +n_(DMRS))modN _(E-PHICH) ^(group) +I _(PHICH) N _(E-PHICH) ^(group)  (12)n _(E-PHICH) ^(seq)=(└I _(PRB) _(_) _(RA) ^(lowest) ^(_) ^(index) /N_(E-PHICH) ^(group) ┘+n _(DMRS))mod2N _(SF) ^(PHICH)  (13)

There are also cases where multiple E-PDCCH regions exist. For example,in coordinated multi-point (CoMP) scenario 4, each RRH is configuredwith a TP-specific E-PDCCH region. For such cases, it may be necessaryto define a corresponding TP-specific E-PHICH. The TP ID may be used todefine such TP-specific features.

Alternatively, an eNB may semi-statically configure whether the PHICH orthe E-PHICH is used. If a UE (either advanced or legacy) is configuredto decode the PHICH in the legacy PDCCH region, the UE may use theformulas as defined in Rel-10 to derive the E-PHICH group and sequenceindex:n _(PHICH) ^(group)=(I _(PRB) _(_) _(RA) ^(lowest) ^(_) ^(index) +n_(DMRS))modN _(PHICH) ^(group) +I _(PHICH) N _(E-PHICH) ^(group)  (14)n _(PHICH) ^(seq)=(└I _(PRB) _(_) _(RA) ^(lowest) ^(_) ^(index) /N_(PHICH) ^(group) ┘+n _(DMRS))mod2N _(SF) ^(PHICH)  (15)

If an advanced UE is configured to decode the E-PHICH, the UE may usethe following formula to derive the E-PHICH group and sequence index asdefined below:n _(E-PHICH) ^(group)=(I _(PRB) _(_) _(RA) ^(lowest) ^(_) ^(index) +n_(DMRS))modN _(E-PHICH) ^(group) +I _(PHICH) N _(E-PHICH) ^(group)  (16)n _(E-PHICH) ^(seq)=(└I _(PRB) _(_) _(RA) ^(lowest) ^(_) ^(index) /N_(E-PHICH) ^(group) ┘+n _(DMRS))mod2N _(E-SF) ^(PHICH)  (17)where parameters for the E-PHICH, such as the number of the E-PHICHgroup N_(E-PHICH) ^(group) and the spreading length N_(E-SF) ^(PHICH),may be signaled to the UE through higher layer signaling or other meanssuch as the PBCH. By doing this, the PHICH and E-PHICH configurationsmay be separated, which may ease implementation.

If a UE monitors only the E-PDCCH, complications may arise in enablingthe UE to receive both the PHICH and the E-PHICH. In addition, the UEmay not receive the PHICH correctly if interference is high in thelegacy region. Therefore, the UE may receive the E-PHICH only when theUE is configured to monitor only the E-PDCCH. Alternatively, the eNB mayperform configuration separately whether the UE receives the PHICH ornot.

If a UE is configured to receive the E-PHICH, then the phich-configfield carried in the MIB may be re-interpreted for E-PHICH resourceconfiguration, as shown below.

PHICH-Config ::= SEQUENCE {    phich-Duration     ENUMERATED {normal,extended},    phich-Resource     ENUMERATED {oneSixth, half, one,    two} }

When ‘phich-Duration’ is equal to ‘normal’, then the E-PHICH may residein the OFDM symbols carrying the DMRS and/or the REs close to the DMRSREs in the first slot only, as illustrated in FIG. 14(a). When‘phich-Duration’ is equal to ‘extended’, then the E-PHICH may spread tothe OFDM symbols carrying the DMRS and/or the REs close to the DMRS REsin the both the first and the second slot of a subframe, as illustratedin FIG. 14(b).

The ‘phich-Resource’ field can be used for calculating the number ofE-PHICH groups as for the PHICH, resulting in the same amount ofresources allocated for the E-PHICH and the PHICH. If it is desired toallocate more resources to the E-PHICH than the PHICH, then the value of‘phich-Resource’ can be re-interpreted for the E-PHICH. This can happen,for example, when a large number of UEs need to be served while thePHICH is not available (e.g., if there is no legacy control region). Forexample, if ‘ENUMERATED {oneSixth, half, one, two}’ is re-interpreted byan advanced UE which corresponds to N_(g) ϵ{⅓, 1, 2, 4}, then the numberof groups in the E-PHICH may be twice that of the PHICH.

Alternatively, the PBCH may still contain the information only for thePHICH. A UE may receive information about the PHICH from the PBCH andstart to monitor and receive the PHICH first. The UE may be configuredto monitor and receive the E-PHICH semi-statically through higher layersignaling. Such a configuration may be sent together or separately withthe configuration of the E-PDCCH. After such a configuration isreceived, the UE may start to monitor and receive the E-PHICH.

As mentioned previously, a fourth set of embodiments deals withinter-cell interference management for the E-PHICH. The inter-cellinterference coordination (ICIC) mechanism may be leveraged to achieveinterference avoidance between the E-PHICHs of neighbor cells in thefrequency domain. That is, two neighbor cells may transmit E-PHICHs overnon-overlapping PRBs. This implies that the E-PHICH resource is keyedoff an ICIC parameter. To coordinate between cells of two eNBs, a signalmay be exchanged over the X2 interface between two neighbor cells, andthe E-PHICH resource parameter may be signaled to the connected UEs viaa system information block (SIB). The X2 signaling as defined in Rel-8for ICIC may be reused to achieve this coordination after resources forE-PHICH transmission are allocated. Before such a parameter is receivedby the UE, the UE may monitor the PHICH only. For an RRH scenario, theX2 exchange may not be needed to coordinate two RRHs of the same eNB.Thus, the eNB scheduler may define such a PHICH resource parameterwithout any dependency on X2 signaling. The E-PHICH resource unit may beshifted based on cell ID, so that E-PHICHs from different cells do notcollide. Such a shift could be REG-based or PRB-based.

While interference avoidance may be desirable, interferencerandomization in the design of the E-PHICH may still be needed for oneor more reasons. First, the neighbor cells may not always choose tocoordinate (e.g., two cells may belong to two different operators).Second, there may be a preparation period before the cells arecoordinated. Third, full coordination may be difficult if the bandwidthis small and/or if coordination needs to be done between multiple cells.One example of providing interference randomization is a case where theREG resources for the E-PHICH vary as a function of the subframe numberas well as the cell ID so that two cells would be likely to usedifferent REGs in a given subframe.

At least two different scenarios may exist regarding inter-cellinterference management for the E-PHICH. In a first scenario, acomponent carrier (CC) has a legacy control region on the downlink, andthe associated uplink CC may or may not be cross-carrier scheduled. Inthis case, the UE may receive a downlink ACK/NACK via the PHICH only inthe legacy control region, when the UE attaches initially. When thenetwork directs the UE to receive an ACK/NACK via the E-PHICH only viaUE-specific RRC signaling, the UE may switch to receive the E-PHICH onlyfor all future subframes until further notice. The UE-specific RRCsignaling may carry resource allocation information for the E-PHICH sothat the UE can locate the E-PHICH directly for future subframes.Information carried on the UE-specific RRC signaling may include the PRBlocation of the E-PHICH, which takes into account the interferencecoordination between two neighboring cells or two neighboring RRHs. Thesame UE-specific RRC signaling may also trigger the UE to receive adownlink control channel via the E-PDCCH. When the network directs theUE to stop detecting the E-PHICH, then the UE may switch to receive thePHICH only for all future subframes until further notice.

In the second scenario, a component carrier, CC_(B), that has no legacycontrol region on the downlink is associated with another componentcarrier, CC_(A), that has a legacy control region. In this case, the UEmay receive a downlink ACK/NACK via the PHICH only in the legacy controlregion of CC_(A), when the UE attaches initially. When the network addsCC_(B) to the UE as a secondary cell (SCell), the UE may start toreceive all downlink control signals only on CC_(B). This implies thatthe UE switches to receive the E-PHICH (and E-PDCCH) only on CC_(B) forall future subframes until further notice. There may be no need todetect the PDCCH and the PHICH on CC_(B) because the PDCCH and the PHICHare not transmitted on CC_(B). The eNB may need to configure the E-PHICH(and E-PDCCH) on CC_(B) before CC_(B) is added as an SCell, as CC_(B)may experience less interference from other cells or TPs. When thenetwork removes CC_(B) from the UE's SCell list, the UE may switch toreceive downlink control channels only on CC_(A) for all futuresubframes until further notice.

The embodiments disclosed herein provide a detailed multiplexing schemefor the E-PHICH and the E-PDCCH and/or PDSCH. Alternatively, the E-PHICHmay be transmitted alone in some PRBs. Consequently, the embodiments canachieve efficient resource utilization for the E-PHICH given thecharacteristic of the E-PDCCH and/or PDSCH. The embodiments also provideefficient utilization of PHICH resources by using a concept of multiplePHICH resource sets. The embodiments further enable a UE to receiveHARQ-ACK when both the PHICH and the E-PHICH are supported in an LTEeNB. In addition, the embodiments provide ICIC management for theE-PHICH that can avoid interference on the E-PHICH.

The above may be implemented by a network element. A simplified networkelement is shown with regard to FIG. 16. In FIG. 16, network element3110 includes a processor 3120 and a communications subsystem 3130,where the processor 3120 and communications subsystem 3130 cooperate toperform the methods described above.

Further, the above may be implemented by a UE. An example of a UE isdescribed below with regard to FIG. 17. UE 3200 may comprise a two-waywireless communication device having voice and data communicationcapabilities. In some embodiments, voice communication capabilities areoptional. The UE 3200 generally has the capability to communicate withother computer systems on the Internet. Depending on the exactfunctionality provided, the UE 3200 may be referred to as a datamessaging device, a two-way pager, a wireless e-mail device, a cellulartelephone with data messaging capabilities, a wireless Internetappliance, a wireless device, a smart phone, a mobile device, or a datacommunication device, as examples.

Where the UE 3200 is enabled for two-way communication, it mayincorporate a communication subsystem 3211, including a receiver 3212and a transmitter 3214, as well as associated components such as one ormore antenna elements 3216 and 3218, local oscillators (LOs) 3213, and aprocessing module such as a digital signal processor (DSP) 3220. Theparticular design of the communication subsystem 3211 may be dependentupon the communication network in which the UE 3200 is intended tooperate.

Network access requirements may also vary depending upon the type ofnetwork 3219. In some networks, network access is associated with asubscriber or user of the UE 3200. The UE 3200 may require a removableuser identity module (RUIM) or a subscriber identity module (SIM) cardin order to operate on a network. The SIM/RUIM interface 3244 istypically similar to a card slot into which a SIM/RUIM card may beinserted. The SIM/RUIM card may have memory and may hold many keyconfigurations 3251 and other information 3253, such as identificationand subscriber-related information.

When required network registration or activation procedures have beencompleted, the UE 3200 may send and receive communication signals overthe network 3219. As illustrated, the network 3219 may consist ofmultiple base stations communicating with the UE 3200.

Signals received by antenna 3216 through communication network 3219 areinput to receiver 3212, which may perform such common receiver functionsas signal amplification, frequency down conversion, filtering, channelselection, and the like. Analog to digital (A/D) conversion of areceived signal allows more complex communication functions, such asdemodulation and decoding to be performed in the DSP 3220. In a similarmanner, signals to be transmitted are processed, including modulationand encoding for example, by DSP 3220 and are input to transmitter 3214for digital to analog (D/A) conversion, frequency up conversion,filtering, amplification, and transmission over the communicationnetwork 3219 via antenna 3218. DSP 3220 not only processes communicationsignals but also provides for receiver and transmitter control. Forexample, the gains applied to communication signals in receiver 3212 andtransmitter 3214 may be adaptively controlled through automatic gaincontrol algorithms implemented in DSP 3220.

The UE 3200 generally includes a processor 3238 which controls theoverall operation of the device. Communication functions, including dataand voice communications, are performed through communication subsystem3211. Processor 3238 also interacts with further device subsystems suchas the display 3222, flash memory 3224, random access memory (RAM) 3226,auxiliary input/output (I/O) subsystems 3228, serial port 3230, one ormore keyboards or keypads 3232, speaker 3234, microphone 3236, othercommunication subsystem 3240 such as a short-range communicationssubsystem, and any other device subsystems generally designated as 3242.Serial port 3230 may include a USB port or other port currently known ordeveloped in the future.

Some of the illustrated subsystems perform communication-relatedfunctions, whereas other subsystems may provide “resident” or on-devicefunctions. Notably, some subsystems, such as keyboard 3232 and display3222, for example, may be used for both communication-related functions,such as entering a text message for transmission over a communicationnetwork, and device-resident functions, such as a calculator or tasklist.

Operating system software used by the processor 3238 may be stored in apersistent store such as flash memory 3224, which may instead be aread-only memory (ROM) or similar storage element (not shown). Theoperating system, specific device applications, or parts thereof, may betemporarily loaded into a volatile memory such as RAM 3226. Receivedcommunication signals may also be stored in RAM 3226.

As shown, flash memory 3224 may be segregated into different areas forboth computer programs 3258 and program data storage 3250, 3252, 3254and 3256. These different storage types indicate that each program mayallocate a portion of flash memory 3224 for their own data storagerequirements. Processor 3238, in addition to its operating systemfunctions, may enable execution of software applications on the UE 3200.A predetermined set of applications that control basic operations,including at least data and voice communication applications forexample, may typically be installed on the UE 3200 during manufacturing.Other applications may be installed subsequently or dynamically.

Applications and software may be stored on any computer-readable storagemedium. The computer-readable storage medium may be tangible or in atransitory/non-transitory medium such as optical (e.g., CD, DVD, etc.),magnetic (e.g., tape), or other memory currently known or developed inthe future.

One software application may be a personal information manager (PIM)application having the ability to organize and manage data itemsrelating to the user of the UE 3200 such as, but not limited to, e-mail,calendar events, voice mails, appointments, and task items. One or morememory stores may be available on the UE 3200 to facilitate storage ofPIM data items. Such a PIM application may have the ability to send andreceive data items via the wireless network 3219. Further applicationsmay also be loaded onto the UE 3200 through the network 3219, anauxiliary I/O subsystem 3228, serial port 3230, short-rangecommunications subsystem 3240, or any other suitable subsystem 3242, andinstalled by a user in the RAM 3226 or a non-volatile store (not shown)for execution by the processor 3238. Such flexibility in applicationinstallation may increase the functionality of the UE 3200 and mayprovide enhanced on-device functions, communication-related functions,or both. For example, secure communication applications may enableelectronic commerce functions and other such financial transactions tobe performed using the UE 3200.

In a data communication mode, a received signal such as a text messageor web page download may be processed by the communication subsystem3211 and input to the processor 3238, which may further process thereceived signal for output to the display 3222, or alternatively to anauxiliary I/O device 3228.

A user of the UE 3200 may also compose data items, such as emailmessages for example, using the keyboard 3232, which may be a completealphanumeric keyboard or telephone-type keypad, among others, inconjunction with the display 3222 and possibly an auxiliary I/O device3228. Such composed items may then be transmitted over a communicationnetwork through the communication subsystem 3211.

For voice communications, overall operation of the UE 3200 is similar,except that received signals may typically be output to a speaker 3234and signals for transmission may be generated by a microphone 3236.Alternative voice or audio I/O subsystems, such as a voice messagerecording subsystem, may also be implemented on the UE 3200. Althoughvoice or audio signal output may be accomplished primarily through thespeaker 3234, display 3222 may also be used to provide an indication ofthe identity of a calling party, the duration of a voice call, or othervoice call-related information, for example.

Serial port 3230 may be implemented in a personal digital assistant(PDA)-type device for which synchronization with a user's desktopcomputer (not shown) may be desirable, but such a port is an optionaldevice component. Such a port 3230 may enable a user to set preferencesthrough an external device or software application and may extend thecapabilities of the UE 3200 by providing for information or softwaredownloads to the UE 3200 other than through a wireless communicationnetwork. The alternate download path may, for example, be used to loadan encryption key onto the UE 3200 through a direct and thus reliableand trusted connection to thereby enable secure device communication.Serial port 3230 may further be used to connect the device to a computerto act as a modem.

Other communications subsystems 3240, such as a short-rangecommunications subsystem, are further optional components which mayprovide for communication between the UE 3200 and different systems ordevices, which need not necessarily be similar devices. For example, thesubsystem 3240 may include an infrared device and associated circuitsand components or a Bluetooth™ communication module to provide forcommunication with similarly enabled systems and devices. Subsystem 3240may further include non-cellular communications such as WiFi, WiMAX,near field communication (NFC), and/or radio frequency identification(RFID). The other communications element 3240 may also be used tocommunicate with auxiliary devices such as tablet displays, keyboards orprojectors.

The UE and other components described above might include a processingcomponent that is capable of executing instructions related to theactions described above. FIG. 18 illustrates an example of a system 3300that includes a processing component 3310 suitable for implementing oneor more embodiments disclosed herein. In addition to the processor 3310(which may be referred to as a central processor unit or CPU), thesystem 3300 might include network connectivity devices 3320, randomaccess memory (RAM) 3330, read only memory (ROM) 3340, secondary storage3350, and input/output (I/O) devices 3360. These components mightcommunicate with one another via a bus 3370. In some cases, some ofthese components may not be present or may be combined in variouscombinations with one another or with other components not shown. Thesecomponents might be located in a single physical entity or in more thanone physical entity. Any actions described herein as being taken by theprocessor 3310 might be taken by the processor 3310 alone or by theprocessor 3310 in conjunction with one or more components shown or notshown in the drawing, such as a digital signal processor (DSP) 3380.Although the DSP 3380 is shown as a separate component, the DSP 3380might be incorporated into the processor 3310.

The processor 3310 executes instructions, codes, computer programs, orscripts that it might access from the network connectivity devices 3320,RAM 3330, ROM 3340, or secondary storage 3350 (which might includevarious disk-based systems such as hard disk, floppy disk, or opticaldisk). While only one CPU 3310 is shown, multiple processors may bepresent. Thus, while instructions may be discussed as being executed bya processor, the instructions may be executed simultaneously, serially,or otherwise by one or multiple processors. The processor 3310 may beimplemented as one or more CPU chips.

The network connectivity devices 3320 may take the form of modems, modembanks, Ethernet devices, universal serial bus (USB) interface devices,serial interfaces, token ring devices, fiber distributed data interface(FDDI) devices, wireless local area network (WLAN) devices, radiotransceiver devices such as code division multiple access (CDMA)devices, global system for mobile communications (GSM) radio transceiverdevices, universal mobile telecommunications system (UMTS) radiotransceiver devices, long term evolution (LTE) radio transceiverdevices, worldwide interoperability for microwave access (WiMAX)devices, and/or other well-known devices for connecting to networks.These network connectivity devices 3320 may enable the processor 3310 tocommunicate with the Internet or one or more telecommunications networksor other networks from which the processor 3310 might receiveinformation or to which the processor 3310 might output information. Thenetwork connectivity devices 3320 might also include one or moretransceiver components 3325 capable of transmitting and/or receivingdata wirelessly.

The RAM 3330 might be used to store volatile data and perhaps to storeinstructions that are executed by the processor 3310. The ROM 3340 is anon-volatile memory device that typically has a smaller memory capacitythan the memory capacity of the secondary storage 3350. ROM 3340 mightbe used to store instructions and perhaps data that are read duringexecution of the instructions. Access to both RAM 3330 and ROM 3340 istypically faster than to secondary storage 3350. The secondary storage3350 is typically comprised of one or more disk drives or tape drivesand might be used for non-volatile storage of data or as an over-flowdata storage device if RAM 3330 is not large enough to hold all workingdata. Secondary storage 3350 may be used to store programs that areloaded into RAM 3330 when such programs are selected for execution.

The I/O devices 3360 may include liquid crystal displays (LCDs), touchscreen displays, keyboards, keypads, switches, dials, mice, track balls,voice recognizers, card readers, paper tape readers, printers, videomonitors, or other well-known input/output devices. Also, thetransceiver 3325 might be considered to be a component of the I/Odevices 3360 instead of or in addition to being a component of thenetwork connectivity devices 3320.

The following are incorporated herein by reference for all purposes:3GPP TS 36.211, 3GPP TS 36.212, and 3GPP TS 36.213.

In an embodiment, a method for communication in a wirelesstelecommunication system is provided. The method comprises generating,by a network element, a sequence of signals of an E-PHICH. The methodfurther comprises mapping, by the network element, the sequence ofsignals of the E-PHICH to a first set of resource elements, wherein thefirst set of resource elements is multiplexed with a second set ofresource elements over a set of virtual resource blocks, and wherein thesecond set of resource elements carries at least one of an E-PDCCH and aPDSCH.

In another embodiment, a network element is provided. The networkelement comprises a processor configured such that the network elementgenerates a sequence of signals of an E-PHICH. The processor is furtherconfigured such that the network element maps the sequence of signals ofthe E-PHICH to a first set of resource elements, wherein the first setof resource elements is multiplexed with a second set of resourceelements over a set of virtual resource blocks, and wherein the secondset of resource elements carries at least one of an E-PDCCH and a PDSCH.

In another embodiment, a UE is provided. The UE comprises a processorconfigured such that the UE receives a sequence of signals of anE-PHICH, wherein the sequence of signals has been mapped to a first setof resource elements, and wherein the first set of resource elements hasbeen multiplexed with a second set of resource elements over a set ofvirtual resource blocks, and wherein the second set of resource elementscarries at least one of an E-PDCCH and a PDSCH.

In another embodiment, a method for communication in a wirelesstelecommunication system is provided. The method comprises providing, bya network element, one or more E-PHICH resource sets, wherein an E-PHICHresource set contains a plurality of E-PHICH resources, and wherein anindex of an E-PHICH resource used in transmitting an E-PHICH is relatedto a parameter associated with a PUSCH.

In another embodiment, a network element is provided. The networkelement comprises a processor configured such that the network elementprovides one or more E-PHICH resource sets, wherein an E-PHICH resourceset contains a plurality of E-PHICH resources, and wherein an index ofan E-PHICH resource used in transmitting an E-PHICH is related to aparameter associated with a PUSCH.

In another embodiment, a method for communication in a wirelesstelecommunication system is provided. The method comprises monitoring,by a UE, both a PHICH and an E-PHICH transmitted by a network element,wherein a resource index of the E-PHICH is related to a parameter of aPUSCH.

In another embodiment, a UE is provided. The UE comprises a processorconfigured such that the UE monitors both a PHICH and an E-PHICHtransmitted by a network element, wherein a resource index of theE-PHICH is related to a parameter of a PUSCH.

In another embodiment, a method for communication in a wirelesstelecommunication system is provided. The method comprises sending, by afirst network element, to a second network element, a message on themapping of a resource set of a first E-PHICH to physical resources. Themethod further comprises transmitting, by the first network element, toa UE, the first E-PHICH.

In another embodiment, a network element is provided. The networkelement comprises a processor configured such that the network elementtransmits a first E-PHICH. The processor is further configured such thatthe network element coordinates with another network element in mappingto physical resources a resource set of the first E-PHICH and a resourceset of a second E-PHICH transmitted by the other network element.

The embodiments described herein are examples of structures, systems ormethods having elements corresponding to elements of the techniques ofthis application. This written description may enable those skilled inthe art to make and use embodiments having alternative elements thatlikewise correspond to the elements of the techniques of thisapplication. The intended scope of the techniques of this applicationthus includes other structures, systems or methods that do not differfrom the techniques of this application as described herein, and furtherincludes other structures, systems or methods with insubstantialdifferences from the techniques of this application as described herein.

While several embodiments have been provided in the present disclosure,it should be understood that the disclosed systems and methods may beembodied in many other specific forms without departing from the scopeof the present disclosure. The present examples are to be considered asillustrative and not restrictive, and the intention is not to be limitedto the details given herein. For example, the various elements orcomponents may be combined or integrated in another system or certainfeatures may be omitted, or not implemented.

Also, techniques, systems, subsystems and methods described andillustrated in the various embodiments as discrete or separate may becombined or integrated with other systems, modules, techniques, ormethods without departing from the scope of the present disclosure.Other items shown or discussed as coupled or directly coupled orcommunicating with each other may be indirectly coupled or communicatingthrough some interface, device, or intermediate component, whetherelectrically, mechanically, or otherwise. Other examples of changes,substitutions, and alterations are ascertainable by one skilled in theart and could be made without departing from the spirit and scopedisclosed herein.

What is claimed is:
 1. A method for communication in a wirelesstelecommunication system, the method comprising: monitoring, by a userequipment (UE), both a physical hybrid automatic repeat request (HARQ)indicator channel (PHICH) and an enhanced PHICH (E-PHICH) transmitted bya network element; and determining, by the UE, whether the PHICH or theE-PHICH is being used to assign resources, wherein the UE determineswhether the PHICH or the E-PHICH is being used based on a number ofPHICH groups and a number of E-PHICH groups, wherein the number of PHICHgroups is indicated in a physical broadcast channel (PBCH), and whereinthe number of E-PHICH groups is indicated via one of higher layersignaling or in unused bits within the PBCH.
 2. The method of claim 1,further comprising: comparing, by the UE, the number of PHICH groupswith the number of E-PHICH groups; and determining, by the UE, that theE-PHICH is being used to assign resources if the number of PHICH groupsis greater than or equal to the number of E-PHICH groups.
 3. The methodof claim 1, further comprising determining, by the UE, whether the PHICHor the E-PHICH is being used depending on whether a physical uplinkshared channel (PUSCH) physical resource block (PRB) index and ademodulation reference signal (DMRS) value satisfy certain criteria. 4.The method of claim 1, further comprising monitoring, by the UE, boththe PHICH and the E-PHICH in a downlink subframe.
 5. The method of claim1, further comprising monitoring, by the UE, only the E-PHICH in adownlink subframe where the PHICH is not monitored.
 6. The method ofclaim 1, further comprising receiving, by the UE, UE-specific radioresource control (RRC) signaling from the network element that directsthe UE to receive an acknowledgement/negative acknowledgement (ACK/NACK)only via the E-PHICH, wherein the UE-specific RRC signaling carriesresource allocation information for the E-PHICH, and wherein theUE-specific RRC signaling triggers the UE to receive a downlink controlchannel via an enhanced physical downlink control channel (E-PDCCH). 7.The method of claim 1, further comprising: receiving, by the UE,UE-specific radio resource control (RRC) signaling from the networkelement that directs the UE to stop monitoring the E-PHICH; andmonitoring, by the UE, only the PHICH in response to receiving theUE-specific RRC signaling.
 8. A user equipment (UE) comprising: at leastone memory device; and a processor configured to execute instructionsstored on the at least one memory device such that when executed, theUE: monitors both a physical hybrid automatic repeat request (HARQ)indicator channel (PHICH) and an enhanced PHICH (E-PHICH) transmitted bya network element; determines whether the PHICH or the E-PHICH is beingused to assign resources; and monitors only the PHICH or the E-PHICH inresponse to receiving signaling that directs the UE to stop monitoringthe E-PHICH or the PHICH, respectively.
 9. The UE of claim 8, whereinthe UE determines whether the PHICH or the E-PHICH is being used basedat least on a physical uplink shared channel (PUSCH) physical resourceblock (PRB) index.
 10. The UE of claim 9, wherein all PHICH and E-PHICHresources are jointly mapped to the PUSCH PRB index.
 11. The UE of claim8, wherein the PHICH is used when an uplink downlink control information(DCI) grant is transmitted on a physical downlink control channel(PDCCH), and wherein the E-PHICH is used when the uplink DCI grant istransmitted on an enhanced PDCCH (E-PDCCH).
 12. The UE of claim 11,wherein: when the uplink DCI grant is transmitted on the PDCCH, the UEcalculates a PHICH group index using the following formula:n _(PHICH) ^(group)=(I _(PRB) _(_) _(RA) ^(lowest) ^(_) ^(index) +n_(DMRS))mod N _(PHICH) ^(group) +I _(PHICH) N _(PHICH) ^(group);andn _(PHICH) ^(seq)=(└I _(PRB) _(_) _(RA) ^(lowest) ^(_) ^(index) /N_(PHICH) ^(group) ┘+n _(DMRS))mod2N _(SF) ^(PHICH) when the uplink DCIgrant is transmitted on the E-PDCCH, the UE calculates the PHICH groupindex using the following formula:n _(E-PHICH) ^(group)=(I _(PRB) _(_) _(RA) ^(lowest) ^(_) ^(index) +n_(DMRS))mod N _(E-PHICH) ^(group) +I _(PHICH) N _(E-PHICH) ^(group)n _(E-PHICH) ^(seq)=(└I _(PRB) _(_) _(RA) ^(lowest) ^(_) ^(index) /N_(E-PHICH) ^(group) ┘+n _(DMRS))mod 2N _(SF) ^(PHICH).
 13. The UE ofclaim 8, wherein, when the UE is configured to decode the E-PHICH, theUE derives an E-PHICH group number and a sequence index using thefollowing formula:n _(E-PHICH) ^(group)=(I _(PRB) _(_) _(RA) ^(lowest) ^(_) ^(index) +n_(DMRS))modN _(E-PHICH) ^(group) +I _(PHICH) N _(E-PHICH) ^(group)n _(E-PHICH) ^(seq)=(└I _(PRB) _(_) _(RA) ^(lowest) ^(_) ^(index) /N_(E-PHICH) ^(group) ┘+n _(DMRS))mod 2N _(E-SF) ^(PHICH).
 14. The UE ofclaim 8, wherein the UE monitors a downlink acknowledgement/negativeacknowledgement (ACK/NACK) response only via the PHICH in a legacycontrol region when the UE initially attaches to the network element.15. The UE of claim 8, wherein a resource set of the E-PHICH in asubframe relates to a variable sent to a plurality of UEs by the networkelement.
 16. The UE of claim 15, wherein a first value of the variableindicates that the resource set resides in a first slot of a subframeonly, and a second value of the variable indicates that the resource setspans a first slot and a second slot of a subframe.
 17. The UE of claim8, wherein the PHICH is used to carry a HARQ-ACK response when a relateduplink downlink control information (DCI) grant is transmitted on aphysical downlink control channel (PDCCH), and the E-PHICH is used tocarry the HARQ-ACK response when a related uplink DCI grant istransmitted on an enhanced PDCCH (E-PDCCH).
 18. The UE of claim 8,wherein a resource set of the E-PHICH is defined independently of aresource set of the PHICH.
 19. The UE of claim 8, wherein: when thenetwork element adds the second component carrier to the UE as asecondary cell, the UE starts to receive HARQ-ACK responses related touplink data transmission on the second component carrier via a downlinkchannel of the second component carrier, wherein the network elementconfigures the E-PHICH on the second component carrier before the secondcomponent carrier is added as a secondary cell; and when the networkelement removes the second component carrier from the UE's secondarycell list, the UE switches to receiving HARQ-ACK response uplink datatransmission on the second component carrier via a downlink channel ofthe first component carrier.
 20. A non-transitory computer mediumstoring computer readable instructions executable by a processor toimplement a method for communication in a wireless telecommunicationsystem, the method comprising: monitoring, by a user equipment (UE),both a physical hybrid automatic repeat request (HARQ) indicator channel(PHICH) and an enhanced PHICH (E-PHICH) transmitted by a networkelement; determining, by the UE, whether the PHICH or the E-PHICH isbeing used to assign resources; and monitoring, by the UE, only thePHICH or the E-PHICH in response to receiving signaling that directs theUE to stop monitoring the E-PHICH or the PHICH, respectively.